Flags for C++ compilers

CMakeLists.txt

if(WIN32)
  set(TARGET_WINDOWS TRUE)
  if(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
    set(CXX_MSVC TRUE)
  elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
    set(CXX_MINGW TRUE)
  elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
    set(CXX_CLANG TRUE)
  endif()
elseif(UNIX AND NOT APPLE)
  set(TARGET_LINUX TRUE)
  if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
    set(CXX_GCC TRUE)
  elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
    set(CXX_CLANG TRUE)
  endif()
elseif(APPLE)
  set(TARGET_APPLE TRUE)
  if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
    set(CXX_GCC TRUE)
  elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
    set(CXX_CLANG TRUE)
  endif()
endif()

if(CXX_MSVC)
  set(PROJECT_CXX_FLAGS
      /W4
      /external
      /W0
      /external:anglebrackets
      /permissive-
      /wd4619
      /w14242
      /w14254
      /w14263
      /w14265
      /w14287
      /we4289
      /w14296
      /w14311
      /w14545
      /w14546
      /w14547
      /w14549
      /w14555
      /w14640
      /w14826
      /w14905
      /w14906
      /w14928
      /we4834)
elseif(CXX_GCC OR CXX_MINGW)
  set(PROJECT_CXX_FLAGS
      -fuse-ld=lld
      -pipe
      -Wall
      -Wextra
      -Wpedantic
      -Wshadow
      -Wnon-virtual-dtor
      -Wold-style-cast
      -Wcast-align
      -Wunused
      -Woverloaded-virtual
      -Wconversion
      -Wsign-conversion
      -Wnull-dereference
      -Wdouble-promotion
      -Wformat=2
      -Weffc++
      -Wuseless-cast
      -Wlogical-op
      -Wduplicated-branches
      -Wduplicated-cond
      -Wmisleading-indentation
      -Wswitch-enum
      -Werror=format-security
      -Wl,-z,defs)
elseif(CXX_CLANG)
  set(PROJECT_CXX_FLAGS
      -fuse-ld=lld
      -pipe
      -Weverything
      -Wno-c++98-compat
      -Wno-c++98-compat-pedantic
      -Wno-c++98-c++11-compat
      -Wno-c++98-c++11-compat-binary-literal
      -Wno-c++98-c++11-c++14-compat
      -Wno-exit-time-destructors
      -Wno-missing-prototypes
      -Wno-documentation
      -Wno-documentation-unknown-command
      -Werror=format-security
      -Wl,-z,defs)
endif()

if(CXX_GCC OR CXX_MINGW OR CXX_CLANG)
  set(PROJECT_DEBUG_FLAGS
      -g3
      -gsplit-dwarf)
  set(PROJECT_RELEASE_FLAGS
      -flto)
  set(PROJECT_EXE_FLAGS
      -fno-semantic-interposition
      -Wl,--as-needed
      -Wl,-Bsymbolic-functions)
  set(PROJECT_SO_FLAGS
      -fvisibility=hidden
      -fno-semantic-interposition
      -Wl,--as-needed
      -Wl,-Bsymbolic-functions
      -Wl,-z,defs)
  set(PROJECT_HARDEN_FLAGS
      -O2
      -D_FORTIFY_SOURCE=2
      -D_GLIBCXX_ASSERTIONS
      -fasynchronous-unwind-tables
      -fno-plt
      -fstack-clash-protection
      -fstack-protector-strong
      -Wl,-z,relro
      -fcf-protection
      -Wl,--no-copy-dt-needed-entries)
endif()

cxxflags.txt

# For every project

## Clang

-fuse-ld=lld
-pipe
-Weverything
-Wno-c++98-compat
-Wno-c++98-compat-pedantic
-Wno-c++98-c++11-compat
-Wno-c++98-c++11-compat-binary-literal
-Wno-c++98-c++11-c++14-compat
-Wno-exit-time-destructors
-Wno-missing-prototypes
-Wno-documentation
-Wno-documentation-unknown-command
-Werror=format-security
-Wl,-z,defs

## GCC

-fuse-ld=lld
-pipe
-Wall
-Wextra
-Wpedantic
-Wshadow
-Wnon-virtual-dtor
-Wold-style-cast
-Wcast-align
-Wunused
-Woverloaded-virtual
-Wconversion
-Wsign-conversion
-Wnull-dereference
-Wdouble-promotion
-Wformat=2
-Weffc++
-Wuseless-cast
-Wlogical-op
-Wduplicated-branches
-Wduplicated-cond
-Wmisleading-indentation
-Wswitch-enum
-Werror=format-security
-Wl,-z,defs

## MSVC

/W4
/external
/W0
/external:anglebrackets
/permissive-
/wd4619
/w14242
/w14254
/w14263
/w14265
/w14287
/we4289
/w14296
/w14311
/w14545
/w14546
/w14547
/w14549
/w14555
/w14640
/w14826
/w14905
/w14906
/w14928
/we4834


# For debug builds

## GCC/Clang

-g3
-gsplit-dwarf


# For release builds

## GCC/Clang

-flto


# For executables

## GCC/Clang

-fno-semantic-interposition
-Wl,--as-needed
-Wl,-Bsymbolic-functions


# For shared libraries

## GCC/Clang

-fvisibility=hidden
-fno-semantic-interposition
-Wl,--as-needed
-Wl,-Bsymbolic-functions
-Wl,-z,defs


# For hardened builds

## GCC/Clang

-D_FORTIFY_SOURCE=2
-D_GLIBCXX_ASSERTIONS
-fasynchronous-unwind-tables
-fpie -Wl,-pie (for executables)
-fpic -shared (for shared libraries)
-fno-plt
-fplugin=annobin (optional, requires annobin)
-fstack-clash-protection
-fstack-protector-strong
-Wl,-z,relro
-fcf-protection
-Wl,--no-copy-dt-needed-entries